Spark-plug.



A. SCHMIDT.

SPARK PLUG.

APPL'CA 118 917. 1,241,561. Patented Oct. 2,1917.

UNITED STATES PATENT OFFICE.

ALBERT SCHMIDT, OF FLINT, MICHIGAN. ASSIGNOR T0 CHAMPION IGNITION COMPANY. OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN- SPARK-PLUG.

Specification of Letters Patent.

Patented Oct. 2, 1917.

Application filed January 18, 1917. Serial No. 143,149.

To all whom it may concern:

Be it known that I, ALBERT SCHMIDT, a citizen of the Republic of France, residing at Flint, in the county of Genesee and State of Michigan, have invented certain new and useful Improvements, in Spark- Plugs, of which the following is a specification, reference being had therein to the accompanying drawings.

The invention relates to spark plugs and has more particular reference to the means employed for protecting the insulator from the combustion heat. To this end the invention consists in the construction as heremafter set forth.

In the drawings:

Figure 1 is a longitudinal section through a spark-plug embodying my invention;

Fig. 2 is an inner end elevation thereof;

Fig. 2 is a cross-section on line cc--w Fig. 1.

In the present state of the art, it 1s common to form spark-plugs with insulators tapering at their inner ends and inclosed in a casing having straight cylindrical walls. Where such constructions are used on high speed internal combustion engines, the flame which is forced into the cylindrical recess in contact with the tapering insulator will rapidly heat the latter to a temperature where there is danger of preignition. With the present construction this defect is avoided by forming the inner end of the casing of a shape corresponding to the tapering form of the insulator, so as to limit the volume of hot gas which can come into contact with the insulator surface. As specifically shown, A is the insulator having the enlarged portion B, with a shoulder C seated on a gasket D on an opposed shoulder E of the casing F. The insulator is also rovided with a tapering portion G beyond t e shoulder C and extending to the inner end where the insulated electrode H is exposed. The casing F is formed with a threaded nipple I engaging the water-jacketed engine casing, and the walls of this nipple portion are tapered corresponding to the taper of the portion G so as to leave a uniform space between the insulator and the surrounding case.

With the construction as described, during explosion the flame will be forced inward through the restricted annular space J between the inner end of the insulator and the casing and will travel inward until the compression is equal to the impelling force. Inasmuch, however, as the space between the insulator and the case is limited to the minimum required for proper insulation and to prevent short circuiting by sooting, the amount of hot gas thus forced inward isconsiderably less than in a construction where there is a larger opening. Furthermore by reason of the tapering form the insulator is constantly enlarging so as to provide an increasing cross-section for the conduction of the heat. Still further, the construction is one in which a relatively large gasket D may be used, which will conduct the heat from the insulator to the surrounding case, while this gasket itself is protected from exposure to the flame by the contracting walls of the case surrounding the tapering portion of the insulator. Thus the amount of heat which will be imparted to the insulator is reduced and provision is made for conducting away such heat as does enter.

\Vhat I claim as my invention is:

1. In a spark-plug, the combination with an insulator having a tapering inner end, of a casing surrounding said insulator, having the recesses therein correspondingly tapered, said casing being slightly spaced from said insulator to leave a restricted annular space.

2. In a spark-plug, the combination with an insulator having a shouldered portion and a tapering inner end extending therefrom, of a casing having an opposed shoulder providing a seat for the shouldered portion of the insulator, said casing being also provided with a tapering recess surrounding and corresponding to the tapering portion of the insulator.

3. In a spark-plug, the combination with an insulator having a tapering inner end portion and an enlargement providing a shoulder beyond said ta cring portion, of a. casing having a shoul er opposed to the shoulder on the insulator, a gasket forming a bearing and seal for the insulator on the casing, and said casing having a tapering recess surrounding and corresponding to the taper of the insulator, to restrict the volume of space within the casing exposed to the flame.

4. In a spark-plug, a casing having a shouldered portion and a threaded nipple, 5. In a spark-plug, a. casing having its the nipple portionJgaving a, taperin recess nipple portion provided with a, recess tapertherein, of an insulator seated on sai shouling from its outerend toward its inner end, 10 dered portion and having a. ta. ering inner and an insulator within said tapering re- 5 end portion fitting within an uniformly pess.

spaced from the walls of said tapering re- In testimony whereof I aflix m si ature. oess, for the purpose described. ALBERT S IDT. 

